SI

(International System of Units)

(modern metric system)

SI indicates the International System of Units,
the current well-accepted metric units.
The system offers refined definitions for a basic set of units
(meter, kilogram, second, kelvin, mole, and candela)
and a system of derived units.
The most common metric units predate the system
and are also in other similar metric-based systems.
Some other non-SI units remain in common use,
especially for electromagnetic measurement,
such as for magnetic flux density:
in addition to the SI unit, the tesla,
a non-SI (CGS) unit, the gauss, is still in use.